1. Field of the Invention
The present invention relates to a constant speed traveling control apparatus for a vehicle and, more particularly, to a constant speed traveling apparatus having an inter-vehicle distance adjustment function for performing vehicle traveling control while keeping a proper inter-vehicle distance to a vehicle traveling ahead.
2. Description of the Related Art
A vehicle having a constant speed traveling control apparatus will travel at a preset speed even if a driver does not perform a drive operation. When a vehicle subjected to constant speed traveling control at a preset vehicle speed recognizes a vehicle traveling ahead, it measures an inter-vehicle distance to the vehicle traveling ahead, and controls the traveling speed of the vehicle in correspondence with the measured inter-vehicle distance so as to keep a proper inter-vehicle distance to the vehicle ahead. A constant speed traveling apparatus for automatically controlling and varying the vehicle speed when a vehicle traveling ahead is found is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 3-220028.
In this traveling control apparatus, a target traveling speed is calculated on the basis of a preset condition in correspondence with the measured inter-vehicle distance. A control condition for increasing or decreasing the traveling speed of the self vehicle is discriminated from a deviation between the current vehicle speed and the calculated target vehicle speed. Acceleration/deceleration control is made on the basis of the discriminated control condition. However, if the inter-vehicle distance is unnecessarily large, another vehicle may break in between a vehicle traveling ahead and the self vehicle. In this case, the inter-vehicle distance is immediately decreased, and the vehicle therefore undergoes abrupt deceleration in correspondence with the decreased inter-vehicle distance, thus giving considerable discomfort to a driver.
In a vehicle constant speed traveling apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 63-269736, an apparatus obtained by adding an inter-vehicle distance adjustment function to a constant speed traveling control system is proposed. In this apparatus, if the current inter-vehicle distance is 30 m or more, constant speed traveling control is made; if it is less than 30 m, inter-vehicle distance adjustment control for keeping a constant inter-vehicle distance is made.
More specifically, in the constant speed traveling control mode, the throttle opening degree is controlled on the basis of a deviation between the target vehicle speed and the current vehicle speed, while in the inter-vehicle distance adjustment control mode for keeping a constant inter-vehicle distance, the throttle opening degree is controlled on the basis of a deviation between the target inter-vehicle distance and the current inter-vehicle distance.
However, a throttle opening degree control logic for making constant speed traveling control for stably traveling a vehicle at a preset speed, and a throttle opening degree control logic for performing vehicle speed control for keeping a constant inter-vehicle distance use different control parameters. Therefore, this device requires a function which maintains coordination between the two modes to make a smooth transition therebetween. This operation will be described in detail below.
During traveling, sensations experienced by a driver is an acceleration/deceleration caused by a change in throttle opening degree. Therefore, when the throttle opening degree control logic is different, and an actual opening/closing state of a throttle valve is different even in an identical traveling state, a driver feels a different traveling sensation. For this reason, throttle opening degree calculation parameters of the two modes must be adjusted in advance, so that a change in throttle opening degree obtained when a driver changes a set vehicle speed from 80 km/h to 85 km/h in the constant speed traveling control becomes the same as a change in throttle opening degree obtained when the same change in speed occurs in the inter-vehicle distance adjustment control for keeping a constant inter-vehicle distance. If this adjustment is not performed, a driver experiences different traveling sensations in the constant speed control mode and in the inter-vehicle distance adjustment control mode.
In this pre-adjustment, control parameters are adjusted so as to obtain the same frequency and step response characteristics of a control system. Finally, traveling sensations experienced must be actually checked in a test using actual vehicles. The constant speed traveling control apparatus has already been widely spread, and many drivers have become accustomed to its traveling feeling. In consideration of such situation, the throttle opening degree calculation parameters of the inter-vehicle distance adjustment control for keeping an inter-vehicle distance must be adjusted to ensure that the traveling sensation of this control coincides with that of the constant speed traveling control previously used.
However, when the control parameters of the throttle opening degree calculation portion are adjusted, characteristics required for the inter-vehicle distance adjustment control do not always coincide with those required for the constant speed traveling control. If these characteristics do not coincide with each other, processing for correcting another factor (e.g., correcting a target inter-vehicle distance) is required. More specifically, when an operation for causing traveling sensations of the two different control modes to coincide with each other is performed, the development load is increased as compared to a case wherein an identical throttle opening degree calculation is used, and inter-vehicle distance adjustment control characteristics required for keeping a constant inter-vehicle distance may not be realized. For this purpose, new correction processing must be added.
When the inter-vehicle distance to a vehicle ahead is infinity, i.e., when it is determined that no vehicle is present ahead of the self vehicle, acceleration control is adjusted to a preset vehicle speed. In this case, if a set acceleration is small, a long time is required until the vehicle speed returns to the set vehicle speed, thus giving discomfort to a driver. When a set acceleration is large, the self vehicle may immediately approach a vehicle ahead under the acceleration control in consideration of a situation that the detection mechanism erroneously determines that no vehicle is present ahead of the self vehicle even though, in fact, a vehicle is travelling ahead of the self vehicle.